The decision to replace the much-maligned Pro40 League with a 20-team English Premier League from 2010 means Twenty20 cricket will be played in England in four of the six summer months traditionally set aside for the domestic calendar, but concerns about overkill were played down yesterday as county cricket braced itself for a new era which could bring up to £60m a year through broadcasting deals and sponsorship.

The announcement confirmed what had become obvious in the days since proposals for a nine-franchise EPL, drawn up by Keith Bradshaw of the MCC and David Stewart of Surrey, were leaked to the press last Friday: namely, that many of the 18 first-class counties were unwilling to be marginalised and the ECB did not want to cede ownership of a potential milch cow to an outside company, in this case New Twenty20 Ltd. It has also been pointed out that any ECB-sanctioned tournament involving anything but all 18 counties would have been unconstitutional in any case.

However, two of the four competitions in the new domestic structure will now be played in Twenty20 format, and the Worcestershire chief executive, Mark Newton, conceded yesterday that "Twenty20 overkill was the biggest worry we had as a group".

Newton went on: "Most of the chief executives liked 40-over cricket but it is not played anywhere else in the world, so it makes economic and financial sense to play a tournament that would attract others. Overkill is always a possibility and we knew that there was a danger of 'After the Lord Mayor's Show' about this, but that's evolution for you."

Tom Sears, the Derbyshire chief executive who spoke out strongly against a nine-team tournament, was relieved that the ECB had settled for an arrangement which had found favour with most of the chief executives at their most recent meeting.

"Any competition that involves all 18 sides is welcomed by us and it's a significant improvement on what was proposed by Messrs Bradshaw and Stewart," he said. "Overkill is something that could be levelled at the EPL but if the ECB gets it right it could develop a great deal of interest. We are also pleased with plans to spread the Twenty20 league out over a few months. We found that to squeeze in five home games in 14 days or sometimes less was a big ask during this season's Twenty20 Cup."

The ECB chairman, Giles Clarke, said he was "delighted that the board unanimously supported these creative proposals" and spoke of "enormous broadcast and sponsor interest from around the world". In a nod to diplomacy, an ECB press release also declared that the plans take "advantage of elements of the David Stewart and Keith Bradshaw funding proposals", which may refer to nothing more than a universal desire to see wealthy investors support the project.

The press release quoted Stewart as describing the proposals as "extremely exciting and satisfying", but it is clear that not everyone is enamoured of the ECB's reluctance to adopt a plan that would have allowed investors part-ownership of franchises, and with it a greater incentive to write more eye-catching cheques.

Surrey, Lancashire and Hampshire all put their names on Friday's leaked proposal but - in an indication of the current mood of suspicion that prevails in some quarters of English cricket - no one would voice any frustration on the record. It did not require much reading between the lines to understand what those frustrations were, and there are fears now that investors who had originally been attracted by Bradshaw and Stewart's proposal will lose interest. But the charge of self-interest was denied by Newton.

"Lots of people say there are too many counties but we have a track record and there is an affinity with us," he said. "Don't forget it was the counties in 2003 who drove through Twenty20 against the odds, and now it's been developed on the international stage. And it was the counties who in the 1960s developed one-day cricket. We have been moving the game along more than any other country and more than any other group of administrators.

"My first reaction is very positive. The proposal is similar to what the chief executives came up with at last week's meeting. The positives are that we have an EPL in June but we keep the County Championship as it is. The 50-over competition has to be played for the sake of England."

Support for the new structure also came from Derek Brewer, who as chief executive of Nottinghamshire presides over one of the nine counties playing their home fixtures at a so-called Category A ground - the proposed venues for the Bradshaw-Stewart plan.

"Overkill was always something we have to bear in mind but what we saw this season at Trent Bridge was a real thirst for Twenty20 and one of the problems is that we've been staging games in a short and concertinaed period," Brewer said. "A lot of members said 'We'd love to see more but we'd like it spread out'." Not for the first time, the members got their wish.

The EPL explained

· A new English Premier League to be played in June from 2010, involving all 18 first-class counties plus two teams from overseas, possibly South Africa and Australia

· The EPL to be split into divisions one and two, with each division containing 10 teams and each team playing nine matches

· Leagues to be decided by performances in the 2009 Twenty20 Cup

· Twenty20 league involving all 18 counties to be played in July, August and September, mainly on Friday nights

· Structure to mirror the current Twenty20 Cup, with three groups of six providing four semi-finalists

· The two finalists will qualify for the international Champions League

· The 16-match, two-division county championship will remain the same

· The Pro40 League will be scrapped after 2009 but a 50-over competition will be retained